In chemistry, processes in which gas-liquid reactions are involved are extremely numerous, To ensure the contact between a liquid often containing a solid suspended catalyst and the reacting gas, quite a number of different techniques can be used. The usual solutions resort either to the agitation of the liquid by the gas itself, or to the introduction of the gas into a reactor equipped with a mechanical stirrer, or further to a gas-liquid contactor of the ejector type. However, owing to the complexity of the parameters influencing reactions in a heterogeneous medium, such as the rate of transfer of the products involved in the desired reaction at the interface (mass transfer), the hydrodynamic behaviour of the medium and its capacity to maintain suspended a heterogeneous catalyst, the deactivation of the latter in the absence of a saturation by the reacting gas and the important thermal phenomena (heat transfer) taking place, the construction of a high performance reador is always difficult, most of all when secondary or parallel reactions occur which affect the selectivity of the overall process. These synthesis reactions, in particular catalysed hydrogenation, are very often carried out under pressures which can reach 100 bar and temperatures varying between 30.degree. and 300.degree. C., and this places constraints on the equipment to be used and poses considerable problems, in particular in industrial plants, where one must ensure high standards of safety and reliability, and low maintenance costs.